Many appliances use time for control and display purposes. For example, a video cassette recorder (VCR) maintains an internal clock (time reference) in order to permit the user to program the VCR to record a future programming event. That is, using the internal clock, the VCR will automatically turn on, record a future program, and turn off at the end of the program recording time. As an additional feature, the VCR may display the current time and day of the week. A major problem is setting and maintaining the correct time so that the programmability feature will work properly.
Setting the internal clock of a VCR to the correct time and day is often a tedious procedure. Furthermore, the clock may need to be set more than once. In particular, an interruption in power will often result in the loss of clock data requiring that the user re-enter the current time and day into the VCR clock timer. Also, during the change to daylight savings time and back again twice a year, the time of day needs to be re-entered into the VCR internal clock. Other appliances which use time for control and display purposes have similar problems.